1. Field of the invention
The present invention relates to an acoustic vibrator member used in a loudspeaker and the like, and to a method of manufacturing the vibrator member.
2. Description of the Prior Art
It is usually required that an acoustic vibrator member be lightweight and have a low density and a high rigidness. It is also required that the vibrator member have a pertinent large internal loss and that the propagation velocity .rho.E/.sqroot. of the vibrator member be large in Which E represents the Young's modulus and .sqroot. represents the density. A conventional vibrator member is made of a material such as paper, synthetic resin and metal.
Since the vibrator member made of paper generally has a large internal loss, a loudspeaker utilizing the paper vibrator member has a relatively constant responsiveness in the sound pressure vs. frequency characteristic. The rigidness of the paper vibrator member is relatively low. The paper vibrator member generates partial vibrations in a low frequency band of the sound pressure vs. frequency characteristic, thereby to deteriorating the properties of transient and distortion of the loudspeaker thereof. The paper vibrator member is too hygroscopic to cause changes of the tome quality of the sound radiated from the loudspeaker using it. The tone quality of the loudspeaker readily suffers from the deterioration caused by the secular changes.
The vibrator member made of metal has a high rigidness and a low internal loss. The sound pressure vs. frequency characteristic of a loudspeaker utilizing the metallic vibrator member has a peak of resonance at a high frequency part thereof because of the low internal loss thereof. It is however difficult to damp the peak of resonance of the metallic vibrator member. When the peak of the resonance is moved away from the audio frequencies, the metallic vibrator member is suitable for loudspeakers for tweeter and midrange in high and middle acoustic frequency ranges, but not for a woofer for the lower frequency ranges.
The vibrator member made of a synthetic resin such as a thermal plastic resin has a low hygroscopicity and a high internal loss. The synthetic resin vibrator members are suitable for various loudspeakers. The physical properties of the loudspeakers using the synthetic resin vibrator members are stable during and after the manufacture thereof.
The synthetic resin vibrator member has a low rigidness similar to the paper vibrator member. A composite vibrator member mainly made of synthetic resin has recently been developed in order to improve the rigidness of the synthetic resin vibrator member. The materials of the composite vibrator member comprises the synthetic resin and fillers such as carbon fiber, graphite powder, mica powder and whisker which are filled and suspended in the synthetic resin. In this case, long carbon fibers are used as the filler. The mica powder consisting of microparticles each having a large aspect ratio is used as the filler.
It is difficult to obtain a composite vibrator member having good color tones and rich color variations through the conventional method of forming such as injection molding, vacuum forming and compression molding, since the fillers are possibly exposed to the surface of the composite vibrator member. The manufacture of a composite vibrator member is restricted in design even with a coating of coloring on the surface thereof resulting in an unsatisfactory composite vibrator member.